The cardiovascular response evoked by tracheal intubation was observed in 20 patients undergoing elective abdominal surgery in whom anaesthesia was induced with either midazolam 0.3 mg/kg or thiopentone 4.5 mg/kg followed by pancuronium 0.1 mg/kg. In the thiopentone group, intubation caused a mean rise in systolic arterial pressure from 141 to 193 mmHg (p less than 0.0005) and in the heart rate-systolic pressure product from 11101 to 21763 (p less than 0.05); 5 minutes later the mean values were still 173 mmHg and 19030 respectively. In the midazolam group systolic arterial pressure and the rate pressure product increased from 138 to 151 mmHg and 10960 to 14267 respectively in response to intubation. These values were significantly lower than the thiopentone group (p less than 0.005 in each case) and were relatively transient and returned to control values within 5 minutes.